1. Field of the Invention
The present invention relates to a plastic bottle having good heat resistance, pressure resistance and mechanical strength, and a process for its production.
2. Description of the Prior Art
Polyester bottles have widely been used as bottles for foods and beverages such as soy sauce or other sauces, as they have high mechanical strength and are chemically stable.
Particularly, bottles made of polyethylene terephthalate have become popular in recent years as bottles for carbonated beverages, as they have a low permeability against gas such as oxygen or carbon dioxide and good transparency.
In a conventional process for the production of polyethylene terephthalate bottles, it is common that bottles obtained by blow stretching are subjected to heat treatment to improve the heat resistance and to prevent the thermal shrinkage. However, merely by such heat treatment, it has been impossible to obtain a plastic bottle having adequate heat resistance, pressure resistance and mechanical strength required for a bottle for carbonated beverages.
For a bottle to be used as a bottle for a carbonated beverage, it is common that the bottle is first filled with a carbonated beverage and sealed and then a shower of hot water at a temperature of about 70.degree. to 80.degree. C. is sprayed on the bottle for about 30 minutes for sterilization. However, in the case of polyethylene terephthalate bottles produced by the conventional processes, when the internal pressure of the bottles is raised by a volume expansion of the carbonated beverage filled in the bottles or by the gasification of the carbonated substance in the beverage, the entire bottles are likely to undergo an expansion or the bottoms thereof are likely to bulge and deform in to a semispherical shape, whereby their outer appearances tend to be extremely impaired to such an extent that they are no longer acceptable for practical purpose.